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Fox 4 Cylinder to V8 Tach

  • Thread starter Thread starter 93CalypsoConvert
  • Start date Start date Feb 22, 2023
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chilsam

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Jul 13, 2022
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cent ill
Jun 5, 2023
#41
  • Jun 5, 2023
  • #41
GREAT thread...does anyone know if there is a diff between CFI tachs ol skool coil fired tachs ? I have a 93 LX that had a 4cyl n it but I put a 84 GT 2.3T n WC T5 in it while using a repinned MERKUR XR4Ti stand alone harness. It runs great but the tach won't register until about 2600 then it jumps up to where it pegs out sometimes n stays pegged until I blip the throttle again but it never registers the r.p.m accurately or just stays at 0???
 

93CalypsoConvert

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#42
  • Jun 5, 2023
  • #42
Where is your tach signal coming from? The coil?
 

chilsam

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Jul 13, 2022
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cent ill
Jun 5, 2023
#43
  • Jun 5, 2023
  • #43
93CalypsoConvert said:
Where is your tach signal coming from? The coil?
Click to expand...
You are correct
 

Mustang5L5

That is…until I whipped out my Bissell
Mod Dude
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#44
  • Jun 5, 2023
  • #44
Forgot. I did a video on this

 
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foxannne

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jacksonville florida
Aug 15, 2023
#45
  • Aug 15, 2023
  • #45
what wattage resistor are you guys running?
 

93CalypsoConvert

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#46
  • Aug 15, 2023
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1/4 watt if I remember correctly
 
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5.090hatch

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Jul 21, 2025
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#47
  • Jul 21, 2025
  • #47
Stumbled on this thread hoping to get my 4cyl tach working with the v8 swap. Car is a '90 and the spare tach I have is also a '90. Both ex 4cyl cars. What I find strange is both tach boards are completely different from the boards I've seen you guys posting here. Am I missing something?

And yes I'm aware I could run aftermarket tach etc but I'd rather this one work if possible lol
 

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General karthief

wonder how much it would cost to ship you a pair
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#48
  • Jul 21, 2025
  • #48
Look for a part nimber, the first thee characters are year/model, set of four I believe are engineering numbers, these seven characters should match both parts, the one or two letters ie: A or AA or AB at the end, AA and AB mean it's an updated version of the A
I believe this to be fairly accurate.
But I may be wrong......
 
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5.090hatch

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#49
  • Jul 22, 2025
  • #49
General karthief said:
Look for a part nimber, the first thee characters are year/model, set of four I believe are engineering numbers, these seven characters should match both parts, the one or two letters ie: A or AA or AB at the end, AA and AB mean it's an updated version of the A
I believe this to be fairly accurate.
But I may be wrong......
Click to expand...
One is an E8ZF and the other F0ZF, so a 1988 and 1990, but both are identical boards? There is also a tag on the back side stating install date I'm assuming. One in May of '89 and October of '89
 

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Mustang5L5

That is…until I whipped out my Bissell
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Feb 18, 2001
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Jul 22, 2025
#50
  • Jul 22, 2025
  • #50
What does the guage face look like?

E8 is a 1988 engineering number, but doesn’t necessarily mean it was made in 1988. Given the may ‘89 sticker, my guess is one is a late ‘89 model year tach (so 87-89) and the Oct of ‘89 is an early 1990 tach (90-93) give that the model year changeover was around Sept.
 
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5.090hatch

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#51
  • Jul 22, 2025
  • #51
Mustang5L5 said:
What does the guage face look like?

E8 is a 1988 engineering number, but doesn’t necessarily mean it was made in 1988. Given the may ‘89 sticker, my guess is one is a late ‘89 model year tach (so 87-89) and the Oct of ‘89 is an early 1990 tach (90-93) give that the model year changeover was around Septth
Click to expand...
This makes sense because one has the notch out of the corner to clear airbag column for 90 and up cars, and the other is straight across, a definite 89 car.

I traced the circuitry on the board to compare where the resistor was changed in the other boards and I think I found it. Will try and change it out tomorrow and test.

I'll post my findings after I test
 

Mustang5L5

That is…until I whipped out my Bissell
Mod Dude
Feb 18, 2001
43,260
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Jul 23, 2025
#52
  • Jul 23, 2025
  • #52
That's why my video above is specific to 87-89. The tech changed slightly in 1990 and since I didn't have any to play with, i was unable to get an info on what to change
 
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5.090hatch

Member
Jul 21, 2025
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Jul 23, 2025
#53
  • Jul 23, 2025
  • #53
Success! Like noted above in this thread it's the resistor wired next to the adjustable potentiometer pot. Changed out the original 64.9k to a 22k ohm. And with a very very last minute before work test it seems to be dead on without comparing to another tach. (Based on what I know the car idles at etc)
 

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